This is a clinical study to test the transport characteristics from serum into human breast milk of three target drugs. Lactating postpartum females will be reruited into the study. These women will have decided to cease nursing and prior to cessation of nursing, they will be administered a single oral dose of Ranitidine of Phamotidine of Nitrofuratoin. Multiple timed samples of blood and breast milk will be obtained and analyzed for these drugs and their metabolytes. Data will be evaluated in terms of diffusional models for transfer of drugs into milk devised by the PI on the basis of studies in rabbits and other animals.